The present invention relates generally to the field of propagation of electromagnetic energy and more specifically to the field of electromagnetic energy amplifying systems and still more specifically to millimeter wave microstrip amplifiers.
In the past it has been the long-established practice to use ferrite circulators to separate the input and output radio frequency signals in devices utilizing diode reflection amplifiers. For frequencies above 30 GHz, Indium phosphide Gunn diodes have been shown to provide the best means for low noise wide-bandwidth amplification. For the past several years the U.S. Navy has been supporting contractor efforts at fabricating both the diodes and circuits towards this end. Generally, these Indium Phosphide amplifiers utilize the diodes in either coaxial or waveguide cavities which are circulator coupled to separate the input from the output. In the 26 to 40 GHz band circulator, deficiencies have been shown to limit the useful bandwidth to about 10 GHz. At frequencies above 40 GHz, circulators become much more limiting.
The use of circulators in diode reflection amplifier applications can be avoided by the use of 3 db quadrature couplers combined with waveguide amplifier stages. Such amplifiers, however, are much more bulky than the integrated circuit hybrid coupled amplifier described in the present application.